A colloquialism common to Canadian dialects, usually being added to the end of a sentence. The spoken tone of the word implies something to the effect of "do you agree?" Yet, the social connotation of the conversation's context usually implies that the speaker assumes that the listener already does agree. Therefore when a listener is presented with the post-sentence interrogative "eh," both responding in affirmation, and not responding at all, is appropriate.

In short, it's a term used to assert one's own opinion while cautiously acknowledging that the listener is of the same opinion.

Example 1:

Guy 1: I was on my ski-doo the other day and I saw a moose eating a bucket of poutine.
Guy 2: Fuck off, eh?

Coming from a Canadian (where the word was made, no duh),
Eh means anything, really, but usually means YES? or RIGHT? It can also mean RIGHT ON or TOTALLY.
You can only use EH at the end of a sentence, though, and make sure you don't make it a part of a sentence (did that make ANY sense?).

Eh can mean many different things, depending on the context and the speaker... It can mean :

Eh = what did you say?
Eh? = what do you think
Eh!! = WOW!!
EH? = what do you mean?
Eh?? = your joking!!!??
EH!! = Hello..you off in the distance!!!
Eh..cmon eh? = asking them to let you pay for it next time.
Eh...uhuh = yes sure!

but in a sentance its meaning depends on the situation...

Speaker 1: Did you see that guy over there?
Speaker 2: eh?
Speaker 1: The guy with the red hat.
Speaker 2: Ya... what about him?
Speaker 1: He pushed that old lady in line.
Speaker 2: How rude eh.
Speaker 1: ya.